Fastening clips formed from spring steel plate are already known, and in the U.S. Pat. No. 3,831,842 (Tamura) there was described and illustrated a rail fastening clip of general U-shape or "hairpin" shape. In that specification the resilience however, which imparted toe pressure to the rail was due to pressure applied between the ends of the upper leaf of the U-shaped spring, the lower leaf being utilised to locate the rail edge, and in some instances apply no pressure at all. If the required toe pressure on the rail foot is achieved with only a small amount of deflection (due to the effective strained portion being short in length), then a small degree of "settling" of a rail will result in excessive loss of toe pressure. This is of importance when resilient pads are used, since such pads are subject to plastic flow over a period of time. It can be shown that the Tamura device necessarily has a relatively small deflection for the required toe pressure. Furthermore, the sign of the bending moment in the Tamura clip reverses intermediate its ends (that is, the outer fibres pass from tension to compression) between the heel of the clip and the holding down bolt, and this necessarily results in loss of efficiency, having regard to the volume of metal in the clip.
A series of studies has indicated that it is usually desirable to have a toe pressure of between 4000 and 5000 pounds applied to a rail foot, that is, between 2000 pounds and 2500 pounds by each fastener, and the main problem which is encountered when flat or nearly flat plates are used (for example as shown in Boyd U.S. Pat. No. 1,998,043) is again that there is but a small amount of deflection which can be imparted to a plate of feasible length to achieve the required loading.
Screw threaded locking members, such as the bolts illustrated in said U.S. Pat. No. 3,831,842 are generally disfavoured by railway engineers because of the likelihood of failure of the means used to prevent the bolts unscrewing, and probability of thread damage. Consequently, the wedge type locking pin as illustrated in said U.S. Pat. No. 1,998,043 is preferred in some instances, but a difficulty is encountered in possible error due to the manufacturing tolerances required to produce the interengaging parts. The sum total of tolerance errors can often represent a relatively large proportion of the total deflection required for deflecting the plates intermediate their ends, and it becomes very difficult to ensure that the toe pressure against the rail foot always lies within the required working range.
One of the objects of this invention therefore, is to provide improvements whereby the deflection of a rail fastener clip is much greater than heretofore, without producing a clip so long and unwieldly as to be impractical. Briefly, this is achieved in two ways in this invention. First of all a rail fastener clip has a lower leg, an upper leg, and an upstanding back portion joining the legs, and is arranged to have a heel (or toe) bear against a tie or base plate, a toe (or heel), or a pair of toes bear up against the upper surface of the rail foot, and a deflection finger or a pair of deflection fingers on an upper return portion of the fastener clip which are deflected downwardly. Thus the additional length of the plate becomes available for strain, thereby increasing the amount of deflection for a given toe load over that which has been used in prior art clips. A second factor which assists in achieving a large range of deflection for the required range of toe pressure (that is, a low spring "rate") is introducing a variation in cross-sectional area of the clip over its length so that there is a high stress, not only at the locality of the clip heel, but also in each of the legs. This is achieved by having a locating aperture extending through one of the legs, and can also be further implemented by having a pair of deflection fingers forming a bifurcate end to the clip, and a pair of clip engaging toes at the other end, again forming the end to a bifurcate shape. Ideally of course, the edge configuration should be so contoured that the stress is constant throughout the entire length of the clip, but with the arrangement described the improvement is so great that there is in practice no need to incur the expense of fully contouring the clip edges.
If a clip is formed to a "hair-pin" shape, as for example in the U.S. specifications of Armstrong (1,839,725) or Cooper et al (1,422,340), the maximum stress occurs at the extremity of the clip, and this progressively reduces away from that one locality. A further factor which assists in achieving a low spring rate in this invention is the use of an upstanding, back portion between the heel of the clip and the upper leg of the clip (a "straight back"). By having a minimum of curvature in the back portion of the clip, there is a minimum of variation of bending moment over that portion, and therefore better use is made of the available spring metal. Not only does this improve the spring rate of the clip, it also reduces the maximum stress in the clip when it is strained downwardly, and this is of major importance when the clip is used under conditions of high stress corrosion.
In one embodiment which was tested, the working range of toe load of 1500 to 2250 pounds was found to be caused by a deflection of between 4 and 6 mm. imparted to the deflection fingers. This compares very favourably with prior art devices, and provides a range which is easily achieved with ordinary manufacturing tolerances.
Most rail fastening clips presently in use are likely to become displaced upon rail creep in a longitudinal direction, due for example to differential expansion or contraction of the rail with respect to its supporting substrate, or by other causes such as dynamic effects, caused by the passage of trains over the rails. Another object of this invention is to provide fastening means which will inhibit movement of the clip even when rail creep takes place. This is achieved by having a rectangular locating block extending upwardly from a rail support and extending through a rectangular locating aperture in the rail clip, which inhibits both relative rotational and translational movement of the clip.